1. Field of the invention
The present invention concerns a completely dry fluid-tight vacuum pump.
2. Description of the prior art
Completely dry pumps of the type with spirals rendered fluid-tight by metal bellows are already known. Pumps of this kind are described in particular in French Pat. Nos. 2,141,402 and 2,153,129 in the name Paul Vulliez and the corresponding patents No. DE-2,225,327 and U.S. Pat. No. 3,802,809. These pumps are capable of discharging at atmospheric pressure whilst achieving a residual limiting vacuum of approximately 10 Pa (10.sup.-1 millibars).
These patents include proposals to associate these dry spiral pumps with synthetic material diaphragm pumps, which makes it possible to achieve a limiting vacuum of approximately 10.sup.-1 Pa (10.sup.-3 millibars). However, this solution is limited to pumping gases compatible with the nature of the synthetic material diaphragm; it is not applicable to the pumping of corrosive or radioactive gases such as those used, for example, in uranium enrichment or thermonuclear fusion processes, where only pumping members made entirely of metal may be used.
Also known are dry vacuum pumps employing alternating compression of metal bellows which, in association with spiral pumps of the aforementioned type, enable corrosive and radioactive gases to be pumped to a limiting vacuum of the same order of magnitude (10.sup.-1 Pa). The performance capabilities of these bellows type pumps are limited, however, due to the residual volumes which inevitably remain in the vicinity of the bellows.
Finally, there are known other types of diaphragm pumps as described, for example, in French Pat. No. 1,457,688 or U.S. Pat. No. 2,021,156.
The devices described in these patents are equipped with one or more rigid rings mounted loosely in the inside fold or folds of the diaphragm. Apart from the disadvantages already mentioned resulting in certain cases from the use of synthetic material diaphragms, the presence of the rings results in rapid wear of the diaphragm making this type of device unsuitable for the applications more particularly envisaged in the context of the invention.
An object of the present invention is a new type vacuum pump the pumping members of which are metal and which offers improved performance. The invention is directed to a new reciprocating dry pump featuring simple and rugged construction and trouble-free operation, achieving high performance in terms of limiting vacuum through virtually total expulsion of the pumped gas on each compression cycle.
The invention is also directed to a reciprocating dry pump which, in association with a dry spiral pump of the aforementioned type, provides for pumping all gases, including corrosive and radioactive gases, with a significant improvement in terms of limiting vacuum and discharge pressure as compared with known dry pumps.